Tip-Enhanced Raman Spectroscopy

Scanning probe microscopy (SPM) utilizes a metal tip to probe the size and shape of samples at atomic dimensions. The tip can be coated with silver or gold, brought close to a sample of molecules, and when excited with a laser the molecules will yield spectra with greatly enhanced Raman signal intensity. This technique is known as tip-enhanced Raman spectroscopy (TERS).

The signal-enhancement mechanism in TERS is the same as in SERS (i.e., surface-enhanced Raman spectroscopy). In SERS, however, the enhancement can be difficult to control and remains spatially limited to stationary nanoparticles or surface features.

TERS overcomes this limitation by successfully confining the signal enhancement to the near-field surrounding the very sharp SPM tip, allowing optical spatial resolution down to ~10 nm. The Raman signal enhancement in TERS can be so strong that single molecules can be detected. TERS excels when studying samples that exhibit heterogeneities on the nanoscale.

TERS-enabled experiments usually employ a scanning probe microscope in concert with either an upright or an inverted confocal laser scanning microscope. A single objective is often utilized for both excitation and detection.

Illustration of a TERS experiment. The incident light is focused onto the tip-sample gap through a long-working-distance microscope objective. The tip-sample distance is achieved via AFM or STM feedback. The backscattered light is collected through the same objective, spectrally filtered, and detected using a spectrograph with a N2(l)-cooled CCD array. Courtesy of Prof. Markus Raschke- JILA, University of Colorado at Boulder, USA.

Application Notes

Tip-Enhanced Raman Scattering (TERS)
Researchers: Samuel Berweger and Prof. Markus Raschke – Department of
Physics, Department of Chemistry, and JILA, University of Colorado at Boulder used Princeton Instruments' camera and spectrograph for their research.